map-diff: replace previous comment

.github/workflows/map-diff.yml

@@ -54,10 +54,17 @@ jobs:
         done
 
         echo "::set-output name=COMMENT_BODY::$comment_body"
+    - name: Find comment
+      uses: peter-evans/find-comment@v2
+      id: fc
+      with:
+        issue-number: ${{ github.event.pull_request.number }}
+        comment-author: 'github-actions[bot]'
     - name: Add comment
       uses: peter-evans/create-or-update-comment@v1.4.5
       with:
         issue-number: ${{ github.event.pull_request.number }}
+        comment-id: ${{ steps.fc.outputs.comment-id }}
         edit-mode: replace
         body: |
           ${{ steps.get-maps-diff.outputs.COMMENT_BODY }}